The present invention concerns a waveguide transition for low reflection transmission of electromagnetic energy between the fundamental wave type of a rectangular waveguide with a distinct cross section and the fundamental wave type of an elliptical waveguide that permits propagation of the fundamental wave type and higher wave types with a longitudinal channel that permits, on at least one part of its length, propagation of higher wave types and includes a number of steps of different cross section following in succession in the transmission direction and with waveguide gates that lead to the longitudinal channel for coupling to higher wave types of the elliptical waveguide.
This type of waveguide transition is known from DE 38 36 545 C2. Such waveguide transitions are used in high frequency transmission lines in which a high frequency wave must be transmitted with low attenuation over long distances.
Waveguides with a unique cross section, i.e., waveguides in which an electromagnetic wave of a given frequency is only capable of propagation in the fundamental wave type, are preferred for a number of transmission purposes, since the excitation of standing waves of higher wave types in them, which can sensitively affect transmission of a transmission line for certain frequencies, is ruled out. Such unique waveguides, however, in turn have much higher attenuation than waveguides with correspondingly larger cross section, so that the latter are preferred for low-attenuation transmission over longer distances. These waveguides, also referred to as transport waveguides, generally have an elliptical cross section, since these exhibit not only lower attenuation relative to rectangular waveguides, but also have particularly good laying and handling properties so that entire waveguide systems with curvatures can be constructed from one part.
A problem in using such xe2x80x9covermodedxe2x80x9d waveguides is that a smaller part of the electromagnetic energy of the fundamental wave type is converted into higher wave types capable of propagation on curvatures and other small interference sites of the waveguide system; the standing waves (resonances) of the higher wave types caused by this can have a sensitive adverse effect on transmission. In order to achieve transmission with high efficiency, it is necessary, for the fundamental wave type of the unique waveguide to be effectively coupled to the fundamental wave type of the transport wave guide, in which excitation of higher wave types in the transition itself is almost suppressed and the higher wave types unavoidably excited in the transport waveguide are effectively attenuated in order to prevent formation of resonances.
With the present invention, a waveguide transition of the type just mentioned is devised in which the higher wave types occurring in the overnoded waveguide system are effectively coupled. Only in this way is almost complete attenuation of these higher wave types possible. This advantage is achieved by providing elliptical steps in the overmoded section of the transition, so that reflections and therefore non-optimal coupling of the higher wave types that occur in a transition from a rectangular to an elliptical cross section because the wave types are not congruent (as in the known transition) are avoided.
By this expedient, all transformation steps in the overmoded section have ellipse-like cross sections.
The transition to an elliptical cross section of the transport waveguides occurs over several steps, in which the number of wave types capable of propagation can increase in each step as a function of its cross-sectional dimensions.
To achieve simple production of the waveguide transition, the waveguide gates that are situated perpendicular to the axis of the transition and sealed with absorbers are preferably arranged in one step. This means that the cross sections of the individual transformation steps are chosen so that the short circuit planes of the wave types on the waveguide gate, whose large cross-sectional dimension is oriented across the axis of the transition, have a spacing of no more than ⅙ of their waveguide wavelength relative to this gate and that the short circuit planes of the wave types on the perpendicular wavegliide gate, whose large dimension lies along the axis of the transition, have a spacing of ? to ? of their waveguide wavelength (preferably about xc2xc) relative to this gate. Such positioning means that the higher wave types of the transport waveguide are effectively coupled.
The waveguide transition preferably has two elongated gates perpendicular to its axis, which are spaced in the direction of the major axis of the elliptical cross section. Two waveguide channels can be connected to these two gates, each of which is connected to arms of a T-piece. Such a design makes it possible to couple a second wave type independently of the fundamental wave type in the transport waveguide with which a second signal can be additionally be transmitted with a transport waveguide decoupled to the signal of the fundamental wave type.
A chamber containing a damping material to dampen the coupled-in wave types is connected to at least one of the gates.
The waveguide transition can be produced in simple fashion by milling the longitudinal channel with a tool guided parallel to the longitudinal axis of the waveguide transition. This makes it possible to keep the number of parts of the waveguide transition limited and thus avoid tightness problems. The tightness of the waveguide transition is significant because waveguide systems are generally operated with a slight overpressure in order to avoid an adverse effect on their function by penetration of moisture.
The entire waveguide transition according to the invention can be made from a single piece in which the gates are milled with a tool guided perpendicular to the longitudinal axis of the waveguide transition. As an alternative it is also possible for the waveguide transition to contain two pieces that join on a surface that intersects the gates. In this manner the length and number of required seals is kept limited and tightness problems are avoided.